[libvirt] [PATCH 1/1] Remove contiguous CPU indexes assumption

[Eric Blake]

On 02/27/2013 05:13 AM, Li Zhang wrote:
> Hi Eric,
> 
> This should belong to bug-fix, could it be pushed to 1.0.3?

Without any test case under 'make check' that exposes the failure, I'm a
bit worried that this might cause regressions on other setups. I'm not
seven sure I even understand the scope of the problem.  Is it something
specific to running a qemu-system-ppc64 emulator (but can be reproduced
on any host architecture), or is it specific to running on a powerpc
host (but happens for any version of qemu-* target architecture), or is
it something else altogether?

We have test framework in place to allow replaying of a QMP JSON
response and seeing how qemu_monitor_json.c deals with it; what I'd
really like to see is a side-by-side comparison of what the QMP
'query-cpus' command returns for a guest with multiple vcpus on a setup
where you are seeing the problem, when compared to a setup that does not
have the issue.  You can get at this with virsh qemu-monitor-command
$dom '{"execute":"query-cpus"}', if that helps.

To help you out, here's what I got for a guest using 3 vcpus on my
x86_64 host machine and using the qemu-kvm binary:

# virsh qemu-monitor-command guest '{"execute":"query-cpus"}'
{"return":[{"current":true,"CPU":0,"pc":1025829,"halted":false,"thread_id":5849},{"current":false,"CPU":1,"pc":1005735,"halted":true,"thread_id":5850},{"current":false,"CPU":2,"pc":1005735,"halted":true,"thread_id":5851}],"id":"libvirt-9"}

That is, your patch might be right, but I have not yet been convinced
that it is right; and while things may currently be broken on ppc, it is
not a recent breakage, so being conservative and either proving the fix
is right (via testsuite addition) or deferring the fix until post 1.0.3
seems like safer alternatives.  Or maybe someone else will chime in and
agree to take it now, without waiting for my desired burden of proof.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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